The present invention relates to an aircraft nacelle incorporating a reinforced connection between an air intake and a powerplant.
An aircraft propulsion unit comprises a nacelle containing, arranged substantially concentrically, a powerplant connected by a pylon to the rest of the aircraft.
As illustrated in FIG. 1, the nacelle comprises at the front an air intake 10 that channels a flow of air towards the powerplant 12, a first part of the incoming air flow, referred to as the primary flow, passing through the powerplant to participate in combustion, the second part of the air flow, referred to as the secondary flow, being driven by a fan and flowing along an annular duct delimited by the interior wall of the nacelle and the exterior wall of the powerplant.
In the remainder of the description, the longitudinal direction corresponds to the direction of the axis of pivoting of the powerplant fan.
The air intake 10 comprises a lip 14 of which the surface in contact with the aerodynamic flows is extended inside the nacelle by an inner duct 16 of substantially circular sections and outside the nacelle by an exterior wall 18 of substantially circular sections. The powerplant comprises a duct 20 that can be positioned in the continuation of the inner duct 16.
As illustrated in FIG. 2, the air intake 10 is connected to the powerplant 12 by a connection which, at the powerplant, comprises a first annular ring flange 22 secured to a second annular ring flange 24 of a panel delimiting the duct 16 or of an intercalated component 26, referred to as a flange, connected to the panel delimiting the duct 16. The two ring flanges 22 and 24 are pressed firmly together at a junction plane 28 substantially perpendicular to the longitudinal direction, and held in this state by connecting elements 30, for example screw fasteners or rivets, which pass through the ring flanges 22, 24 and run parallel to the longitudinal direction.
From a structural standpoint, the air intake 10 comprises a first frame referred to as the front frame 32 connecting the inner duct 16 and the exterior wall 18 delimiting with the lip 14 an annular duct 34 and a second frame referred to as the rear frame 36 connecting the inner duct 16 and the exterior wall 18 near the junction plane 28.
As far as the rear frame is concerned, this reacts the bending forces, rotation forces or other forces applied to the air intake such as, for example, the weight of the air intake, and the loading induced by the aerodynamic flows.
According to one embodiment, the rear frame 36 is connected to the duct 16 directly or via an intercalated component or flange 38 (visible in detail in FIG. 2), one leg of which is connected to the duct 16, the other leg being connected to the rear frame 36.
The rear frame 36 is connected to the exterior wall 18 directly or via a T-section flange 40 (visible in FIG. 1), the rear frame 36 being connected to the upright of the T-section flange, the top of the T resting against the internal face of the exterior wall 18.
According to one embodiment illustrated in document FR-2.904.604, the rear frame comprises a first metal ring, notably made of titanium, which extends over the entire periphery and is connected to the inner duct 16 and a second ring the exterior peripheral edge of which is connected to the exterior wall 18. The first ring at its exterior peripheral edge comprises a zone of overlap with the interior peripheral edge of the second ring. The two rings are joined together by any suitable means in this region of overlap.
In the event of fan blade breakage, the duct 20 of the powerplant has a tendency to deform significantly, this duct being designed to absorb, by deforming, the energy of the broken blades. At the air intake, the inner duct 16 is made of composite material and its mechanical properties are inferior to those of the duct 20 of the powerplant, notably as far as bending strength is concerned.
Hence, in order to limit the risk of dislocation of the panel or panels that make up the inner duct 16 of the air intake, the spread of deformation from the duct 20 of the powerplant towards the inner duct 16 of the air intake needs to be limited.
One first solution is to design a rear frame and/or a connection between the air intake and the powerplant that are capable of deforming in order to absorb some of the energy and thus limit the spread of deformation towards the inner duct 16 of the air intake.
Another solution is to limit the deformation of the inner duct 16 of the air intake by making it more rigid in the zone of connection between the duct of the powerplant. Solutions have been developed for increasing the rigidity of the rear frame and/or of the connection between the air intake and the powerplant.
In order to increase the rigidity of the rear frame, document FR-2.960.856 proposes a reinforced rear frame which comprises a first metal ring the interior edge of which is connected to the interior wall of the air intake and a second ring the exterior edge of which is connected to the exterior wall of the air intake, the two rings being joined together. According to one specific feature of this rear frame, the second ring comprises at least one angular sector made of composite material with at least one box section shape and the first ring comprises a rib running around the entire periphery of the said ring.
To increase the rigidity of the connection between the air intake and the powerplant, one solution is to increase the thicknesses of the ring flanges, to increase the number of connecting elements or the dimensions thereof. However, that solution is unsatisfactory because it does not prevent deformation from occurring between the ring flange 24 and the rest of the inner duct 16 of the air intake, as a bending motion along an axis tangential to the inner duct 16 occurs between the said ring flange and the said duct.